Method of degasifying radiotubes



July 24, 1928. 1,677,900

F. S. M CULLOUGH METHOD OF DEGASIFYING RADIO TUBES Filed May 6, 1925 X?WNVENTOR.

A TTORNEY Y is energized, and this is continued until the PatentedJuly24, 1928.

UNI-TED. STA'VTES PATENT OFFICE.

FREDERICK- s. MoGULIiOUGH, or wILKiNsBUne, PENNSYLVALATIA;

mnrnon or DEGASIFYING namoru'nns;

Application filed May 6. 1925 Serial No. 28,340.

heater. This cathode is generally coated to.

give high emission at relatively low temperatures. I v

In de-gasifying the usual type of-tube, in which the cathode is of thefilament type, in which there is a materially smaller emitting surfacethan in the tube as above described having the full cylindrical cathode,the tube, after being connected on the pump and baked for the necessaryperiod of time, has its cathode heated by the application of thefilament voltage, after which a plate voltage is applied to the tube.With the plate voltage on, the oscillator is energized, that is, theradio frequency coil surrounding the tube in the pumping apparatus tubeclears.

Such a process when applied to tubes of the cylindrical cathode type,where the size and capacity is so much greater than with the usualfilament type cathode tube, the

late current arcsover upon the oscillator eing energized, dislntegratinand vaporizing or melting the high emlssion coating on the cathode andthe cathode itself.

The object of the present invention is to provide a method ofde-gasifying a tube of the cylindrical cathode type efliciently andwithoutinjury to the cathode or the coating thereon.

In the drawing, I have illustrated a partially completed tube of thegeneral type to which the present invention relates.

In the drawing, which is-in general a ver- I -tical section, 5 is theenvelope of the tube having a base stem 6 in which is the sealing tube 7that connects with the vacuum or exhausting line 8.- In the tube is aplate 9, a grid 10, and a cathode 11 carried on a heater element 12. Aradio frequency coil'13 surrounds the tube when it is being pumped.-

This coil is in a suitable high frequency circuit. a

After being connected with the pump line for the desiredperiod duringwhich the tube ma be baked, the baking is discontinued and a voltage isappliedto wires 12 leading to the heater, raising the temperaturetubehavi'ng a low temperature of the heater and driving out thecontained.

gases. 1 After the heater has been energized for a few seconds, until ithas been brought to the glowing temperature, the external coil isenergized, or, as expressed in the art, the oscillator is applied untilthe tube has cleared up and before any potential is put on the tube. Byclearing up I mean that time when the glow inthe tube has practicallyvanished. Then the radio frequency current is shut down, and with theheater still in operation, the plate voltage is applied, and this isapplied until the tube again clears up.

As the tube is quite highly evacuated before the plate voltage isapplied, and as this is done after the oscillator is shut down,

the impedance of the tube when the plate voltage is applied is such thatarcing between the plate. and cathode will not occur.

As it was heretofore considered necessary to apply the plate voltageWhile the oscillator was operating,'and as such operation withcylindrical cathode tubes frequently resulted in arcing, with injury tothe cathode, it will be seen that the present .process is a distinctdeparture therefrom, and at the same time one which gives equallygoodre--.

sults, so'far as driving out gas is concerned,

as does the former method and without dam- I age to the cathode.

In the drawing, A designates diagram- .matically the plate voltagecircuit.

sheet metal cathodes which includes the steps of connecting the tube ina pumping sys-- tem, baking the tube, heating the cathode by energizingits heater from a source of a te rnatmg current, applying an oscillatingfield to the tube while thecathode remains heated, shutting off theoscillating field, alpplyin a plate voltage to the tube while t e cathoe remains heated and after the oscillating field' has been shut down,and then sealing off the tube.

2. A method of de-gasifying an electron tubes having low temperature higemission gh emission v latin oscillating field to the tube cylindricalcathode and a heater therefor which includes the steps of connecting thetube in a pumping system, baking the tube,

energizing the cathode heater, applying an while the cathode heaterremains energized and until the tube clears, then shutting down theoscilfield and keeping the heater energize then applying a plate voltageuntil the tube again clears, andthen sealing off the tube,

3. A method of degasifying an electron tube having a gas absorbentcathodeheater and a sheet metal cathode supported on the 'ing thecathode heater to drive out absor heater which includes the steps ofconnecting the tube to a pumping system, energizd:

e gases, applying an oscillating field to the tube While the cathodeheater-remains energized and until the heater has been substantiallydegasifie'd, then cuttin ofi. the oscillating field while keeping theeater energized, then applying a plate voltage until the tube clears,and sealing ofi the tube.

In testimony whereof I hereunto afiix my signature.

FREDERICK S. MCCULLOUGH.

